The present invention concerns an explosive device with a hollow charge designed for penetrating armor protected by active primary armor.
It is stated, as a reminder, that a hollow charge is basically made up of a rotationally symmetric explosive charge, provided with an open cavity covered by a metallic liner, and a priming device also having rotational symmetry. When detonated by the priming device, the metallic liner of the cavity is projected onto the rotational axis of the charge producing a jet of molten metal, which travels at very high speed along this axis, and a metal slug, travelling more slowly along the same axis, in the same direction as the preceding jet or in the opposite direction.
It is also reminded that, active primary armor is generally an auxiliary armor positioned in front of a conventional armor, referred to as the main armor; this auxiliary armor comprises two plates, usually made of steel a few millimetres thick with a relatively thin layer of explosive sandwiched between them. The primary armor may be multi-layered, that is, it may include several such sandwiches. The primary armor is provided so that when it is hit by a projectile, the head of the latter detonates the explosive layer on penetrating it. The explosion then projects the steel plates towards the projectile, perturbing it and reducing its lethality. In particular, in the case of a hollow charge projectile, the steel plates of the primary armor interfere with the jet of the hollow charge to such an extent that it loses most of its penetrating power against the main armor.
Such active primary armors are frequently used for the protection of armored vehicles, such as combat tanks.
The problem which faces designers of anti-tank munitions is therefore the following: in order to penetrate the main armor, it is preferable to use a very powerful hollow charge capable of penetrating the main armor which is usually very thick, yet, as stated above, hollow charges are particularly vulnerable to the action of active primary armor.
Different solutions are known for resolving this problem.
A first solution consists of greatly increasing the nominal penetrating power of the hollow charge so that its residual penetrating power (after interference by the primary armor) is sufficient. This process is simple but very expensive in terms of hollow charge calibres.
A second solution is the two-stage hollow charge (often referred to as a tandem warhead). The function of the charge which operates first, referred to as the primary warhead, is to neutralize the primary armor:
either by initiating it soon enough before the detonation of the second, or main, warhead, and thus facilitating the elimination of the primary armor plates before the arrival of the jet of the main warhead; PA1 or by penetrating it without igniting it.
In the first case, adjustment of the process is difficult, in particular regarding the delay between the detonation of the two charges, and the implementation of this adjustment complicates the structure of the munitions, in particular those which, designed to be fired from cannons, must withstand very high acceleration. A solution corresponding to the second case is described notably in French patent application no. 2 583 156, which describes means of reducing the effect of the primary warhead. This embodiment, like the preceding one, has the disadvantage of increasing the bulk of the explosive device.
Furthermore, in order to improve the performance of a hollow charge, a known method consists of providing, between the priming device detonator and the explosive charge, a wave shaper, also known as a screen, whose function is to deflect the detonation wave and make it toric. This makes it possible, by varying the waveform and the shape of the cavity, to increase the velocity of the pentrating jet produced by the hollow charge, the explosive yield of the charge, etc.. The form of the screen is determined so that the detonation wave is deflected without substantial power loss, and so as to obtain the desired angle of incidence of this wave on the liner of the cavity. This leads to bulky screens whose length may be one third or one quarter of the length of the explosive charge, which again leads to an increase in bulk of the hollow charge and reduces its efficiency.